A vibration table upon which is mounted a test specimen or the like is connected with vibrators through couplings. The purpose of the vibration table is to investigate the behavior of a building and test specimens in an earthquake, and the couplings must have the following functions and must accomplish these functions satisfactorily:
(1) The force and the amount of displacement of the vibrator must be transmitted to the vibration table positively and without any time delay. From the theoretical standpoint of analyzing vibration, lost motion and friction in the coupling must be minimized. PA0 (2) The vibrators are generally mounted on a foundation and the vibration table makes two- or three-dimentional movement depending upon its function. To this end, the axial force and displacement of the vibrator must be transmitted to the vibration table and must slide within the bearing strokes against the movements perpendicular to the table. In addition, the sliding frictional resistance must be reduced as much as possible. In general, hydrostatic bearings are used. PA0 (3) The construction must be such that even if the position of the vibration table is distorted under vibrations so that the mounting surface is inclined, no excessive force is exerted to the bearings.
There have been devised various types of couplings which connect such vibrators with the vibration table. For instance, there has been available a hydrostatic bearing type coupling c as shown in FIG. 1 which is interposed between a vibration table a and a vibrator b and includes a spherical body d. The coupling c is rotatably and slidably supported, through the spherical body d, by a supporting member e which extends from the vibration table a. A pressurized oil source f is communicated with the bearing surfaces, whereby the hydrostatic bearing is provided.
In this case, the coupling c is connected to the supporting member e on the vibration table a in a cantilever manner. Therefore, there arises no problem concerning the transmission of the axial force of the vibrator and the absorption of the displacement in the directions perpendicular to the direction of the axial force. However, if "wrenching" occurs due to the distortion of the table a, they cannot slide with small frictional resistances because the spherical surface of the body d does not form a hydrostatic bearing.
There has been also devised and demonstrated a coupling which, as shown in FIG. 2, transmits the force through a connecting rod g whose both ends are terminated by spherical shapes.
With this system, however, when the vibrator b causes the vibration table a to move in one direction, the connecting rods g which support the table a are caused to swing as indicated by the double-pointed arrrows. There must be therefore provided a control for cancelling the displacement due to this swinging motion by the motion of other vibrators. As a result, accurate control of the position of the table is difficult.
One of the objects of the present invention is to provide a coupling device which is simple in construction, has small lost motion and is simple in assembly and mounting.
Another object of the present invention is to provide a coupling device which exhibits minimum frictional resistance to every movement, is free of the influence from other vibrators and obtains correct waveforms by a simple control.
Preferred embodiments of the present invention will be described with reference to the accompanying drawings.